Radioactive dating of moon rocks

The discovery gave scientists a tool for dating rocks that contain radioactive elements.Many elements have naturally occurring isotopes, varieties of the element that have different numbers of neutrons in the nucleus.One way to think about the closed system of the crystal is to compare it to an hourglass.The grains of sand in the top half of the hourglass are the radioactive parents, and those falling to the bottom are the stable daughters.Scientists determined the Earth's age using a technique called radiometric dating.

Because all parts of the solar system are thought to have formed at the same time (based on the solar nebula theory), the Earth must be the same age as the moon and meteorites--that is, about 4.6 billion years old.One line of evidence involves rocks from outside the Earth--meteorites and moon rocks.Radiometric dating shows that almost all meteorites are between 4.5 and 4.7 billion years old.Another line of evidence is based on the present-day abundances of the various isotopes of lead found in the Earth's crust. Three of these isotopes (lead 206, 207, 208) result from radioactive decay of isotopes of thorium and uranium.The fourth, lead 204, is not the result of radioactive decay.